1. Field of the Invention
The invention relates to the design and operation of personal computer systems and, more particularly, to techniques for enhancing EMI suppression in an assembly for housing optional ITE mass-storage devices including, but not limited to, CD-ROM drives, DVD drives, magnetic tape backup systems and Zip drives.
2. Description of the Related Art
Contemporary, high-performance personal computer systems typically are required to accommodate numerous kinds of optional ITE (Information Technology Equipment) mass-storage devices, such as CD-ROM drives, DVD drives, magnetic tape backup systems and Zip drives. Generally, these mass-storage devices are installed in a user-accessible mechanical assembly that is disposed within the computer chassis. The mechanical assembly normally includes a number of bays, often three, each of which permits the installation of a mass-storage device of the type alluded to the above. The mass-storage assembly itself may be mechanically and electrically bonded to the front of the personal computer chassis. Frequently, the mechanical design of the optional mass-storage assembly is driven by the daunting requirement to reliably provision the additional mass-storage equipment in the interior of an already densely populated personal computer chassis. Furthermore, the maintenance of adequate air flow through the chassis in order to facilitate dissipation of heat generated by system electronic components and assemblies is a significant collateral design concern. Preoccupation with the aforementioned design constraints has resulted in configurations that fail to adequately address EMI shielding considerations, resulting in ineffective EMI shielding of the mass-storage bay assembly.
Accordingly, what is desired is a mechanism for enhancing the electromagnetic shielding characteristics of the mass-storage bay assembly, without relaxation or disparagement of the prevailing mechanical design criteria. In this regard, and in the manner to be specifically described below, the subject invention adroitly applies waveguide techniques so as to promote the attenuation, both by reflection and absorption, of electromagnetic energy in the mass-storage bay assembly.
Specifically, it is widely understood that a metal aperture with a depth or thickness dimension that is at least equal to the largest cross section dimension of the aperture operates as waveguide beyond frequency cutoff (WBFC). A waveguide so dimensioned attenuates electromagnetic energy both by absorption and reflection. See, for example, D. J. Angelakos, xe2x80x9cRadio Frequency Shielding Properties of Metal Honeycomb Materials and Wire-Mesh Enclosures,xe2x80x9d IEEE EMC Symposium (1960). Common applications of WBFC techniques include honeycomb air vents, control shafts, light pipes, and so forth. U.S. Pat. No. 5,698,818, entitled xe2x80x9cTwo Part Closely Coupled Cross Polarized EMI Shieldxe2x80x9d describes a personal computer chassis that embellishes the WBFC technique with cross-polarized air vents to suppress radiation. Similarly, U.S. Pat. No. 6,252,161, entitled xe2x80x9cEMI Shielding Ventilation Structurexe2x80x9d describes an extruded or a molded conductive air vent constructed from either elastomeric or plastic material. The air vent described therein is based on the WBFC principle and discloses a vent hole pattern that may be inexpensively tailored in both size and shape to simultaneously address both electromagnetic shielding and thermal dissipation requirements. The above-identified patent and patent application are hereby incorporated by reference into this Description.
In general, WBFC configurations are characterized by a waveguide depth that is approximately 3 to 5 times the opening of the aperture. With these dimensional constraints, a shielding effectiveness of between 80 and 100 dB may be realized at operating frequencies below the waveguide cutoff frequency. The subject invention, however, represents an application of the WBFC technique that, although not strictly conforming to the above-stated dimensional constraints, obtains a markedly enhanced level of EMI attenuation that had not heretofore been achievable with respect to mass-storage bay assembly designs.
The above and other objects, advantages and capabilities are achieved in one aspect of the invention by a drive bay for housing optional mass-storage devices, such as CD-ROM drives, DVD drives, magnetic tape backup systems, Zip drives and the like. The drive bay comprises a plurality of sections, each section for housing an individual mass-storage device or other electronic equipment. The drive bay also comprises a plurality of dividers, each of the dividers for dividing a respective section of the drive bay into a plurality of compartments, wherein a cross-sectional dimension of each of the compartments is sufficiently small to provide substantial attenuation of electromagnetic signals up to the highest expected operating frequency of the computer system. In practice, the dividers cause each of the compartments to be dimensioned so as to effectively operate as a waveguide beyond frequency cutoff (WBFC).
In an alternative embodiment, the invention is realized in a computer system that comprises a plurality of option bays for housing electronic assemblies. The option bays are arranged to be at least pairwise contiguous and are configured to have substantially equal height, width and depth dimensions, whereby the respective height and width dimensions of an option bay define a cross-sectional dimension of the bay. Unpopulated option bays also comprise a divider disposed in at least one of the option bays so as to form a plurality of compartments within the bay. Because the cross-sectional dimension of each of the compartments is less than the cross-sectional dimension of the option bay, the compartments afford substantially enhanced attenuation of electromagnetic signals having a frequency at the highest expected operating frequency of the computer system.
A further embodiment is manifested in an option bay assembly for a computer system. The assembly comprises a plurality of option bays for housing electronic assemblies, the option bays are arranged to be at least pairwise contiguous and are configured to have substantially equal height, width and depth dimensions, whereby the respective height and width dimensions of an option bay define a cross-sectional dimension of the bay. The assembly also comprises a divider disposed in at least one of the option bays to form a plurality of compartments within the bay so that the cross-sectional dimension of each of the compartments is less than the cross-sectional dimension of the option bay. The resulting dimensions of the compartments are such that the compartments afford substantially enhanced attenuation of electromagnetic signals having a frequency at the highest expected operating frequency of the computer system.
In another aspect, the invention is practiced in the form of a method of enhancing the EMI shielding characteristics of an assembly for housing mass-storage devices for a personal computer system, wherein the housing includes at least one storage bay that is physically defined by height, width and depth dimensions. The invention comprises dividing the bay into a number of compartments that extend along the depth of the bay. The largest cross-sectional dimension of the compartments is less than one-third the depth of the bay. As a result, each of the compartments operates as a waveguide beyond frequency cutoff at the highest anticipated operating frequency of the computer system.